Numerous devices have already been designed to enable tires to continue to operate during reduced pressure conditions. One typical device is an elastomer ring mounted on the rim of a wheel inside the pneumatic tire fitted to the wheel. The elastomer ring has an annular base clamped onto the tire rim, holding the beads of the tire pressed against rim flanges. The ring has a radially-projecting annular portion extending towards the tire tread which, in the event of a reduced tire pressure, acts to support the underside of the tread, enabling the vehicle operator to continue driving without having to stop immediately to change the tire. U.S. Pat. No. 6,076,578 discloses one such device.
Another type of device is shown in U.S. Pat. No. 6,564,842. The insert is mounted on the tire rim and is not required to contact the tire beads; instead the tire beads are designed to lock into the tire rim during reduced pressure operation. Again, the radially outer surface of the insert supports the underside of the tire during reduced pressure operation.
The goal of both types of rim inserts is to provide the tire with support and enable the vehicle operator to continue to operate the vehicle for at least another 50 km at a safe operating speed. This continued operation gives the operator time to reach a safe location where the tire can be changed.
Several concerns for such devices has been the weight added to the vehicle by the presence of four rim inserts increasing the overall weight of the tire/wheel system, and the durability of the rim insert. Ideally, the rim insert has an optimized reduced weight and an optimized increased durability to withstand the forces to which it will be subjected during run-flat operation.